US8088866B2ActiveUtilityPatentIndex 48

Polyethylene composition for pressure pipes with enhanced flexibility

Assignee: BAECKMAN MATSPriority: Oct 4, 2006Filed: Sep 28, 2007Granted: Jan 3, 2012

Est. expiryOct 4, 2026(~0.3 yrs left)· nominal 20-yr term from priority

Inventors:BAECKMAN MATS AHLSTRAND LARS-ERIK HAGSTRAND PER-OLA PALMLOF MAGNUS

Y10T428/139C08L 23/08C08L 23/06C08F 210/16C08L 2205/02C08L 23/0807C08L 23/04F16L 9/12C08L 2203/18

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Claims

Abstract

The present invention relates to a polyethylene composition comprising a base resin which comprises (a) an ethylene homo- or copolymer fraction (A); and (b) an ethylene homo- or copolymer fraction (B), wherein (i) fraction (A) has a lower weight average molecular weight than fraction (B); (ii) the base resin has a density of 932 to 938 kg/m 3 ; (iii) the polyethylene composition has an MFR 5 of 0.1 to 0.6 g/10 min; and (iv) the polyethylene composition has a shear stress η2.7 kPa of 85 to 230 kPas. Furthermore, the present invention relates to an article, preferably a pipe comprising said composition and to the use of said composition for the production of an article, preferably a pipe.

Claims

exact text as granted — not AI-modified

1. A polyethylene composition comprising a base resin which comprises
 (a) an ethylene homo- or copolymer fraction (A); and 
 (b) an ethylene homo- or copolymer fraction (B), wherein
 (i) fraction (A) has a lower weight average molecular weight than fraction (B); 
 (ii) the base resin has a density of 932 to 938 kg/m 3 ; 
 (iii) the polyethylene composition has an MFR 5  of 0.1 to 0.6 g/10 min; and 
 (iv) the polyethylene composition has a shear stress η 2.7 kPa  (viscosity at a shear stress of 2.7 kPa at 190° C.) of 85 to 230 kPas. 
 
 
     
     
       2. The polyethylene composition according to  claim 1  further comprising a nucleating agent. 
     
     
       3. The polyethylene composition according to  claim 1 , wherein fraction (A) has a MFR 2  of 10 to 400 g/10 min. 
     
     
       4. The polyethylene composition according to  claim 3 , wherein fraction (A) has an MFR 2  of 25 to 100 g/10 min. 
     
     
       5. The polyethylene composition according to  claim 1 , wherein fraction (A) has a density of 960 to 980 kg/m 3 . 
     
     
       6. The polyethylene composition according to  claim 1 , wherein the SHI (2.7/210)  (ratio of the viscosity, measured at a shear stress of 2.7 kPa and 210 kPa at 190° C.) of the polyethylene composition is 10 to 49. 
     
     
       7. The polyethylene composition according to  claim 1 , wherein the flexural modulus of the polyethylene composition is 300 to 700 MPa. 
     
     
       8. The polyethylene composition according to  claim 1 , wherein the weight split between fraction (A) and fraction (B) is (30-47): (70-53). 
     
     
       9. The polyethylene composition according to  claim 1 , wherein the rapid crack propagation resistance of a pipe made of the polyethylene composition as measured in the S4 test results in a T crit  of &lt;−6° C. 
     
     
       10. The polyethylene composition according to  claim 1 , wherein the slow crack propagation resistance of a pipe made of the polyethylene composition as measured according to ISO 13479:1997 is &gt;500 h. 
     
     
       11. The polyethylene composition according to  claim 1 , wherein the base resin comprises 0.2 to 3.0 mol % of at least one alpha-olefin comonomer. 
     
     
       12. The polyethylene composition according to  claim 1 , wherein fraction (B) comprises 0.4 to 6.0 mol % of at least one alpha-olefin comonomer. 
     
     
       13. An article comprising a polyethylene composition according  claim 1 . 
     
     
       14. The article according to  claim 13  wherein the article is a pipe. 
     
     
       15. The pipe according to  claim 14  which fulfils the MRS 8.0 requirement according to ISO 9080. 
     
     
       16. A polyethylene composition comprising a base resin which comprises
 (a) an ethylene homo- or copolymer fraction (A); and 
 (b) an ethylene homo- or copolymer fraction (B), wherein
 (i) fraction (A) has a lower weight average molecular weight than fraction (B); 
 (ii) the base resin has a density of 932 to 938 kg/m 3 ; 
 (iii) the polyethylene composition has an MFR 5  of 0.1 to 0.6 g/10 min; 
 (iv) the polyethylene composition has a shear stress η 2.7 kPa  (viscosity at a shear stress of 2.7 kPa at 190° C.) of 85 to 230 kPas; 
 (v) the SHI(2.7/210) (ratio of the viscosity, measured at a shear stress of 2.7 kPa and 210 kPa at 190° C.) of the polyethylene composition is 15 to 35; and 
 (vi) the flexural modulus of the polyethylene composition is 400 to 700 MPa.

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